The bore-sight direction of an antenna corresponds to an axis of maximum gain (maximum radiated power). In many cases there is a requirement for thin, directional, wideband or even Ultra-Wideband antennas to have suitable bore-sight performance. One such example is used in medical devices, where the bore-sight direction can be configured for use in/on human tissue, either attached against skin for a non-invasive application, or against muscle or any internal tissue/organ for invasive applications.
In prior art directional antennas, the antenna is designed so that a substantial percentage of the antenna's power is typically radiated in the bore-sight direction. However, in such prior art antennas, some residual power (in some cases, up to about 20%) typically radiates in an opposite direction, which is known as “back-lobe” radiation. These prior art antennas typically include a reflector at a distance of λ/4 that allow the energy radiated backwards to be properly reflected towards the main lobe. However, in some instances, upon antenna dimensions or the radiated bandwidth do not allow for such structure, other alternatives must be sought to avoid, for example, out-of-phase interference with the main lobe direction propagating waves, and/or avoid back lobe radiation.